Abstract A convenient solvent purity test that distinguishes between trace organic impurities present in either organic solvents miscible with water or in water is described. It utilizes the reversed-phase liquid chromatographic trace-enrichment technique by which solvent impurities are concentrated onto the inlet end of a reversed- phase column. The complete test procedure consists of a specific series of gradient elution runs conducted under standardized conditions in both the forward and reverse directions after first subjecting different volumes of each pure solvent to trace enrichment. The resulting set of gradient elution profiles produces a wealth of chromatographic information, the interpretation of which enables the origin of impurities present in a binary solvent system to be determined. Tests show that acetonitrile is relatively pure but that trace impurities present in methanol or tetrahydrofuran can exceed and mask those present in water. The efficacies of some treatments designed to remove trace organic impurities from water are evaluated using the solvent purity test.